Observational constraints on dynamical dark energy with pivoting redshift

TL;DR

This study explores how the pivoting redshift in a generalized dark energy model affects observational constraints, revealing degeneracies and correlations that influence the interpretation of dark energy parameters.

Contribution

It introduces the impact of including a free pivoting redshift in the CPL parametrization on dark energy constraints, highlighting the importance of this parameter in cosmological analyses.

Findings

The pivoting redshift remains unconstrained when free, showing degeneracy with $w_0$.

Fixing $z_p$ alters the correlation between $w_0$ and $w_a$, changing from negative to positive.

The cosmological constant remains consistent within 1$\sigma$ for all cases.

Abstract

We investigate the generalized Chevallier-Polarski-Linder (CPL) parametrization, which contains the pivoting redshift $z_p$ as an extra free parameter. We use various data combinations from cosmic microwave background (CMB), baryon acoustic oscillations (BAO), redshift space distortion (RSD), weak lensing (WL), joint light curve analysis (JLA), cosmic chronometers (CC), and we include a Gaussian prior on the Hubble constant value, in order to extract the observational constraints on various quantities. For the case of free $z_p$ we find that for all data combinations it always remains unconstrained, and there is a degeneracy with the current value of the dark energy equation of state $w_0$. For the case where $z_p$ is fixed to specific values, and for the full data combination, we find that with increasing $z_p$ the mean value of $w_0$ slowly moves into the phantom regime, however the cosmological constant is always allowed within 1$\sigma$ confidence-level. However, the significant effect is that with increasing $z_p$ the correlations between $w_0$ and $w_a$ change from negative to positive, with the case $z_p =0.35$ corresponding to no correlation. This feature indeed justifies why a non-zero pivoting redshift should be taken into account.